Electric furnace and method of operating same



. F. T. SNYDER ELECTRICJURNACE AND METHOD 0Fl OPERATlNG SAME.

APPucAUoN man @1.23, ma. x

katamail May 3l, 319m.

2 SHEETS-SHEET 2. q

. be ad 'z'intageously carbon rod.

' tra a ai tiliilTllilt FREDERICK T. SNYDER, Ofc @hl- I HJLTOQ, ASSIGHOR T END'USTRIAL ELECTRIC IBDIANA.

ELETRIC F'UBHACE ANB ME HQE) F OPERATING SAME.

Application tiled @ctober 23, 1913.

To all 'whom t may concern.'

Be it known that l, Fnnoniiioii T. SNYDER, citizen of the YUnited liltates7 residingar at Oak Park, in the county)l of Cook and State of Illinois, have invented a certain new and uset'ul improvement in lllectric Furnaces and Methods of Operating Same, of which the tollowinfbr is a fullj clear, concise., and exact description.

My invention relates to improvements in electric tornar-es. The objects ot my inveiition are: to provide an improved method of automatici lli7 regulating' the electric power supply ot' an electric furnace so as to maintain a uniform temperature in the furnace; to prolong" the lite ot the furnace parts; and to provide a novel construction by means of which the above mentioned method ot regir lation mayv 4be carried out more advantageously than with existing types of furnaces.

In the accompanying' drawing l have shown in Figure l, a diagram by reference to which the 'features and underlying` principles of the invention will be more readily understood. Fig. 2 is a sectional elevation ot an improved torni iii-furnace., in connection with which my improved method may carried out. Figs. J3, 4,75 and 6 are diagrammatic representations of modified forms of the invention.

Before describing a furnace structure ein bodying invention, l shall set forth the underlying principles there-ot by reference to the diagram, Fig-1. As introductory to such description7 I shall explainv the meanH vingot eertain'terms hereinater used.

Ii constant potential supi; ly of alternating' current, as said exi'iression is used here# in7 is one in which the average ot' the Voltage during'eacli. alternation remains the same 'during successi ve altern ations.

The equilibrium temperiitiire of the re.- sistor. as used herein, is the temperature at which the radiation ot heat energy trom the resistor exactly balances the electric input of energy absorbed by the resistor.

A conductor or resistor with a negative temperature coeicient is one in which the resistance decreases with increase of temperature, as, tor example. inthe case of a lt is to be noted that an electric are is a resistor with a negative temperature coethcient, since-the resistance l olithe are Specicaton of Letters Patent.

Patented Serial No. 796,746.

diminishes with increased a ture.

A conductor coeiiicient is a May Si, E19/2li.

verage temperawth a positive tempera-ture conductor in iihich the resistance increases with increase ot temperatures as, for example, a me electric current be wire, the Wire will heat up tal Wire. it an passed through a metal from the resistance to the passage of the current. As the wire becomes hotter than i it will radiate heat. tion, according to the lwell tss surroundings Roughly this radiarecognized law ot Stefans, will vary proportionally to the difference of the ethpower ot the absolute temperatures of the wire and its surroundings. As the wire increases. lilith a constant of electric current this incre diminishes the energy input gets hotter, its resistance' potential source ase ot resistance As the energy input decreases with increased teiniierature,

and the radiation increases,

a temperature wiil be reached at which the energy input and the radiation output will balance and the system w brium at that definite temp ill operate in stable equilierature. Under usual commercial conditions the length and diameter of the reterence to the' potential -rire can be so chosen with of the current supply that the temperature at which the electric input and radiation cutout balance Will be below` the melting;` @table electric heaters are this basis.

it an electric current point ot the wire.

consnucted on be passed through a carbon rod, a conductor haring a negative temperature coeiiicient, troni the resistance to the pa rent. As the rod becomes the 'rod Will heat upl ssage of the curhotter. its radio.n

tion ot heat increases. At the same time the resistance of the rod will decrease. With a constant potential'souree ot electricity,

under' ordinary conditions this will cause more current to flow through the rod, producing` more energy to be radiated. it the surroundings of thel rod be kept fairly cool,

'the amount radiated will increase rapidly with the temperature, owing to Stefan Lith power law. increase of temperature at The resistance decreases with a much slower rate. So that eventually the radiation will catch up with the input and of 'the rod will not rise fur the temperature ther. @Wing to the negative temperature coetlicientfo't' the temperature is carbon, this equilibrium much higher than with a metal Wire having a positive temperature coefficient. lilith a carbon rod exposed to surroundings kept 'fairly cool, the diameter and length oi" the rod can be chosen to reach this equilibrium the energy developed by negative temperature coecient and withY temperature, using ordinary low pressure constant potential voltages7 as, for example, in the case with an incandescent lamp.

Referring novv to VFig. Il? the axis oi the abscissee is a measure o'ltemperature in degreescentigi'ade and also oi current in amperes, While the axis of the ordii'iates is a measure oli electric energy in lrilovvatts and also oir potential in volts. The curve A shows the energy radiated. vlioin a selected -resistor with no heat insulation around it. y In case the selected resistor isla metallic Wire, the line or curve C shows the energy developed. therein when a constant electric potential is applied to the terminals of the wire. The slope of the line C indicates that theenergy input diminishes with increase of the temperature ol the resistor. The intersection of the curves and C inn dicated v.by the point gives vthe equilibrlurn temperature o this resistor, 1n the case' assumed,' or a resistor having a positive temperature coefficient.

ln the diagram, the curve or line F shows a resistor havlng a constant potential applied to its terminals. lt Will'be seen frointhe slope of the line that the energy increases with increase ot' ternfperature. The `point-of intersection` G of this line with the radiation curve A gives be used as a ply) to go to innch Irodgets the equilibrium temperature. 'lt 'will be seen that the equilibrium temperature in the case of a resistor having a negative temperature coefficient is' greater than in the previous case of a ,vireresistor having a ositive temperature coefficient, for the same initial energy input. u 'With electric furnace work, the purpose .is 'to hea-t the material to be treated, usually toa high temperature. lf a carbon rod resistor for this purpose, 1t no radiate to cool surroundings,

in properly built furnaces, 4prevente-d as :far as practical and the heat 's held in the furnace until thetemperature reached. which is required for the material under treatment. This iforces 'the carbon rod. (with. a constantxpotential current suphigher temperatures to the equilibrium temperature. As the htterthe furnacel also gets hotter prevented) and can 1 rediatio' reach {conduction being largely this action further raises 'the -equilibrium temperature until'it goes above the destructionA temperature of the furnace material. That is, Withthe usual commercial conditions, a Ynrnace heated by a resistance having a negative temperature coeilicient, with constant potential current Supply and good last be equal9 they Wasted in iicient in serles Wi h a imanes heat insulation doesnot regulate for any permissible constant temperature, but gets hotter and hotter until the materials oi the furnace break down.

ln the diagram the curve B shows the energy radiated by a resistor inside of an electric furnace provided with good heat in sulatiolfn As the inside of the furnace also is hot, a resistor of given dimensions must go to a much higher temperature to radiate any given amount of energy inside such a furnace than Where it can radiate to cool surroundings. The curve B intersects the line C at a point E representing a temperature very much higher than the point D. Ill a carbon resistor, inside al'urnace baving good heat insulation, be placed in series with a ballast resistance arranged to .operate at substantially constant tempcratureoutside the furnace and the series supplied with electricity at constant potential, the available voltage will divide between the ballast and the carbon resistor in proportion to their resistance. The hot resistance of the carbon resistor may be one third the cold resistance. l'f the cold Y resist- 'ance o1 the carbon resistor and the bal-v Will then divide the voltage equallybetween them and half the energy due to the iowfot the current will be developed by the carbon resistor 1n the 1lurnace and hall' will be wasted by the ballast resistance outside the furnace. lWhen the carbon resistor and the furnace are bot, il the resistance of the carbon resistor be then one-third that oi the constant ballast resistance, the sum oi' the two resistances in series, `when the carbon resistor is hot, will then bev two-thirds of what the sum. Was

when thevcarbon resistor was cold. l/Vith constant potential applied to the series, the flow or ciirrent will be one and one-half times the tiovv that occurred when the resistor was cold. When cold the carbonresistor' absorbs one-hali thel total voltage. l/Vhen hot itabsorbs one-fourth oi' the total voltage. The* other three-'fourths is thus the ballast. with the carbon resistor hot' is one and onehalf times 4the now with carbon resistor cold. Therefore the energy developed by the hot resistor in the furnace (volts multiplied b y ciirrent) is @Gl-:- of the energy developed by the resistor when' cold. That is, the energy sister decreases with increase of temperature While the radiation from the carbon resistor increases as before with increase of temperature. This results in equilibrium be in reached; at a much lower temperature than Where no ballast resistance is 1n series. In the diagram, the curve L` shows a resistor having a negative temperature coefballast resistance.

This line slopes more rapidly than the line supplied to the carbon The current flow y:

C, which latter shows the energy'gdeveloped in a Wire resistor. The inter-section of the line L with the curve B is indicated by they point M and represents a temperature which, while it, is much higher than the temperature indicated by D, is Vneverthev Wasted energy is three-fourths ofthe totalV energy consumed. Under theusual commercial conditions of constant potential distribution voltage and practical furnace dimensions, the amount of the total energy lost in this way makes this matterlof a ballast resistance very uneconomical for temperature regulation. ',Hence l shall now describe the principles underlying a more commercial adaptation of my invention.

If alternating current is 'used from a source of constant potential,v a reactor can be used for ballast instead o'f a resistance.

This has the advantage that the voltage dropvz through the reactor does not lrepresent anv energy loss. This makes it practical, under the usual commercial conditions of constant potential electricity supply and practical furnace dimensions7 to design a resistor that will reach equilibrium temperature corre-' sponding to the usual industrial'requirements. l l

With the `resistor ballast, the Voltage available for the resistor diminishes directly in proportion to the current flow. A ballast reactor has the advantage over the ballast resistance in that the voltage absorbed by the reactor is approximately in quadrature A(90D phase) with4 the voltage left available 'for the resistor.I This latter voltage,.therefore, diminishes more and more rapidly with increase of current flow, so that equilibrium temperature is more promptly reached.

If the proportion of the voltage absorbed by the reactor be made relatively large, the

drop in the rate of input of energy Withincrease of temperature becomes so rapid'that the equilibrium temperatures for an'exposed resistance and for one inclosed in insulating furnace Walls do not differmaterially. ,i

In Fig. l the curve H shows the energy developed by a resistor having a ngative temperature coefficient1 in series with a reactor on a constant potential supply. This curve intersects the radiation curve A at the point' J and it also intersects the radiation.

curveB at the point It will be noted that the latter intersectlon represents atem- `supply with a reactor absorbing 29% of the .lil

perature only slightly higher than the former' temperature and shows that, under these conditins, the equilibrium tempera ture is only slightly higher in an electric furnace Whe-re heat insulation is employed, than with an exposed resistor without heat insulation. v A

Heretofore electric furnaces have been designed to/have as little ieactance in their circuits as possible, great efforts being made, as by interlacingconductors and arranging iron parts to carry small magnetic fields), to reduce the reactance to a minimum. On the c0ntrary,.for the .purposesof my invention, I make thev reactance as large as is commercially practical, ordinarily using a reactance that absorbs not less than 29% of the constantpotential voltagefat the normal full load current of the furnace.

Referring againtoFig. "l, the curve N illustrates 'thevoltage available at the resistor withdiffcrent current fiows, Where the resistor is'in series on a constant potential constantpotentiall voltage, when the furnace isabsorbing its normal full load current. The curve'H is proportional to the corresponding energy,each polnt being the product of the current flowing in the resistor multiplied by the voltage at the terminals of 95 the resistorzfV With any furnacea given current ow with. a given voltage'c'orresponds to a cer.- taiirresistance which mayl befstated in ohms. Part of these ohms of resistance will be in the resistor and part in the reactor. The former may bepdesignated as resistance ohms and the latter as .reactance ohms. ,These `two ohmic quantities vare in quadrature with each other; Under the conditions in which I4 operate my furnacemn the drooping side of the energy'curve, the reactance ohms are larger in number than the resistance ohms.

In Fig. 2 I have illustrated a simple fur-' nace construction with which the foregoing described method may be advantageously carried out. It is to be understood that said method may also be carried out with various types of electric furnaces now in use. The main Walls 1 of the furnace ,are constructed 115 of brick or other heatinsulating material.

The shape and construction of the furnace f .may vary, Within wide limits, in accordance with the particular requirements at hand,

the form illustrated being typical of a furnace wherein the molten bath of metal constitutes one of the electrodes. Theside Walls of the furnace are laminated, being made up' of a. plurality of thin plates or rings 2, 3, of metal having magnetic permeability, as for example the rings or plates may ,be made of steel.' The thickness and the number of the rings or plates employed may'be varied Within a considerable range.v

The laminated rings in thisl construction 1304 suitable conductor 5 passes thfougli "he *of seid furnace,

.'- 'heve been used as in "sponding parts ae iilusti'eted. lt Willybe noted from 'that there ere two points thereon corretively low voltage and at 10W voltage end `high .ment is shown in'lFig. 'the external circuit constituting substanconstitute the magnetic coife of the ieactoi", and are so designed es to insuie the opere.- tion of the furnace onrtlie drooping side ci the energy curve H. ein electrode Li pie jects through the root et the furnace end e being in electi'icel connectionwvith the :molten beth 6 therein. The 'iuinace is supplied with cuirent from en alternating cuiient source "2 thiengh the conductors 8. Undeiceitein conditions en additional ballast reactor' 9 is connected in the external cizcuit. Under other conditions such edditionel reactor is not necessary.

Wiiieice my inventien ceiiied eut in connection with 'furnaces other than with the one deecibed, wherein the ieectoi constiiites part o the furnace construction, ali

et the necessary ieee-tence iney be inserted in the external ciicnit. Such en aime-nge 3,-tlie reactor 9 in the `i-eectence o'i the cii'cnit. 'the saine iefeience ciierecteis Fig. 2 Where cor-fetielly all 'of ln this figur ""5- tlie energy curve ii spending tc each veine oi the kilcwett inpnt, one having e. nigh curient and e rele-- the other keying e low current end e reletiveiy high voltage. rihis permite e heet iny t le furnace to be stertedwith e, long are et high voltage and smell current end nished 'with e slioit eic current. is e 'fee suit of the short are, e. shadow' is thiown on the fooi? ei the uinece by that is, the eiectiode es shield foe the i'ooi, thereby protecting the letter from the heet QI" the eic. iin geneml, by ifeguieting in this menne?, the ieiiectoiy lining is not ingly the useful life o the. 'ininece is 'proionged.

ln making steel in an electric furnace Where it is essential that the composition ci `the metal to be produced shtii be Within eef the furnace terminals so that ciose analytical limits for the different elements, it is important that the fui-nece tem pei'atuie should be maintained .const-ent While making the analysis. As there is no consumption of neat, only the heat. necessary for radiation has' to be supplied 'et this time. This can be accomplished effectively by shortening the arc,

'ens adjustments of the bese I vi6, oi e plurality oi eneifgy supplied to the furnace. The vert eiecini'ode ine-y be mede manually by the attendent whe edjusts the electi'ede in ecoerdence with conM ditions :is indicated by e wett meter.

Heating e cold cha-ige with long e'fc et high voltage and enei'gy input, insiiies rapid melting Without injury te 'the Walls and roof es the heeft eneigy is ebsocbed ieediiy by the compe.' tively coid neige it melts. After it becomesnioiten dei ing the refining operation e short eie low voltage and reduced energy is eni played to economize power end avoid dem, ege to the reiectefy Lining this peiiod when mucii iess heet i maintain 'the molten beth the ieqniied temperature.

The 'variable mite-.ge appli@ sistoi, foereyoiiere desci-"` ineens oi e.'reectencA iii-eilt into tn or .pnt in series in the infnece else be obtained :from high reectencej taking current et conspotentiel and' deliveeinga energy et e. wie :ige *which diops so rapidly above inli uinece current that e further 'incieese eli cuiifent @euses e seduction eneigy absoibecl by the tni'nece. fi circuit taining such e trens'oifmer is indicated gienimeticeiiy in Fig. 'willie tiene compiises primei'yv'windi.. end second ery windings il, the i'enieining pei-ts oei indicated. by ieieence ciieiecteis cotte-- spending to those nreaicnsiy used. 'tee .i/Vliee the constant potentiel eiectiic snp-- ypiy is direct current, 'reactor need. ,El nietain/a. eimiifir iesnit. iio'wevei'. iii-f Ysnppiying; i'lein e conn-foi Weunc; diffect Ci t in wifi the series windin@4 .is so piep@ 'rned connected that the" voltage given by die generato? diepe so sepia iy with ei cuiient How tliet when the 'nirnece op eretedwitii i'iili ined cinii'ent, any .inet-e( in this cuiient wiil reduce the yf? enough 'to yigednce the energy epz" iiui'nece below toll leed. ein elect nace supplied iiein such e. eeinpenn geneiatei" is ii'lustifeted :in 5, 'the etoi' beingn sliown oy the conventie gram l2.'

fin Fig. 6, i. beve. nece snppiied from prises e ieectci l2 e' en eiectiie e ciicnit Wi icf'n cc eny seite-ide i0 in series 'with the i'esiste ef and e'iso in series with the secon-deity windings iai.. i5.. trensioimeis, secondary also conn in series eeen etiiei. The prima windings" 1"( of the i'ensoiinei sie een nested to e suite-ble sonece ei tlnee'piieee elteinating current i8..

The particules 'furnace constinction sciioed above not eniy peirmits et the et windings being;

' Smaii curient, and` tmishiiig the heat KES laminae in cQntact with each Oihei and mi a substantial angle to the lines airing which the heat tends to radiate.

15. The method. of operating im eieeiirie furnace Having reracteiy hee insuistilig Walls and an ae resiswr with a negaiive temperature coefficient, which censisgs in starting :i heat with ieiig are and .nishing he heet with' a shcstef 16. The method of Ope'i'ating eieciic are furnaces, which consists stating 'the fui nace with a long are at high vcitage imi with a Short arc at 10W vciage alud high current.

17. The method of operating an electric furnace having 'efractoy heat insulating Walls, an are resistor Wih si negaebive tems peinture coeiieiezi't, :md suppiied "fi'om a variable voltage source of power, which coi sists in starting a heut with a. long are and finishing the heat 'with zi shorter are.

` 18. The method of opemsng eiectic are furnaces from e. vuriabie voltage seuice of power, which consists in starting; the furnace with a long :irc ai, high voli/ege and smziil current, :m 'finishing the heir*u vwith a short are at low weinige and high current.

'19. The piccess of reiining metal in im eiectric zuc 'furnace which consists iii carrying out the melting pi'ocess with reiurive high voltage und e eorrespcnfiingg long; are :uid then shortening ihe ere Wii'iie ioweiiig the potenifii for the reining p'ecess.

20. The methed of melting and ice'iuiifigA electrode and the meit of en @pasting paris5. 'when e, high Lemme stesi emi. eshei? Lewis refining mi electric me soetweei and subsequeny farming show lower vcizige be'iween said eieciisieg ove? ehe maken mei'zei in reii 21. The method of @pees-iii?? s. "inaee suppiie intil alie are i rem Wifiish consists in iscieasi e cf the are gap 'Within the i maintaining the cuif'ene veine ing pa input is desired eine?. eubsequen' the engch of the :we gap @gj lowei' energy input.

22. The ine-theel of @peste alternating cuifienr. en eecmic a changea?, "with oi.' s-ee'i., .d which 'lienc ik@ assume during; per @if melting peiciud such pesiioii Wi. the charge tha. e. magiieic i into the ciiaiigeg which cciisiisibs in ine. the length Eile el. iig

While. subs'sntia magie charge takes piece, and when i become melted ie-:ueiig iue e, the @painting voimge.

in Witness wheee heifer' my name this eig" eeitii. A. D. 1913. 

